A secular blogger who had been threatened by Islamists was hacked to death in his apartment by a group of unknown assailants, the fourth victim in a series of deadly attacks this year against writers in Bangladesh who have spoken up against Muslim radicalism.

Authorities said Niloy Chakrabati, 40, who went by the pen name Niloy Neel on social networking sites, was slain by men who entered his building after Friday prayers, posing as potential tenants. Hours later, Ansar al-Islam, a local affiliate of Al Qaeda, claimed responsibility.

The death of the blogger, who had favored a ban on Islamist parties, follows the slaying of Ananta Bijoy Das about three months ago by machete-wielding assailants in the northeastern city of Sylhet.

Das wrote for Mukto-Mona, the blog founded by Avijit Roy, a U.S. citizen who was killed in a similar attack outside a book fair in Dhaka, the Bangladeshi capital, in February. A writer who protested Roy’s killing on social media, Washiqur Rahman, was killed in similar fashion on a Dhaka street in March.

Bangladesh, with a history of free expression, is an officially secular country, but more than 90% of its 160 million people are Muslim. In recent months, most secular bloggers here have either gone into hiding or fled abroad. Activists fear that Islamist hit squads have lists of names and addresses of bloggers they intend to kill.

The blogger, slain as his wife was held by the assailants in another room of the apartment, had recently removed photos from his Facebook page and used Kolkata as the current city he was living in. But he had actually remained in Dhaka, where he lived in the flat with his family for the last two years.

Following Das’ murder, Bangaldeshi authorities banned an extremist Islamist group, Ansarullah Bangla Team. The group has claimed responsibility for the initial blogger killings.

In a recent petition, authors including Salman Rushdie and Margaret Atwood called on the nation’s government “to do all in their power to ensure that the tragic events of the last three months are not repeated and to bring the perpetrators to justice.”